Marine borers, particularly, gribbles, and shipworm, have been a scourge on wooden, maritime structures for centuries. Whether pier, dock or hull, given enough time, gribbles and shipworms will literally eat them alive. It was recently estimated that marine borers are causing more that $500 million in damage a year to U.S. waterfronts. In New York City alone, local government is spending in excess of $30 million over a two-year period to address the damage found in lower New York Harbor caused by increased borer activity--one of the negative side effects of cleaner water resulting from environmental improvement programs.
Gribbles, are marine isopod crustaceans; i.e., shrimp-like creatures, that are members of the biological family Limnoria. Typically they are about 5 mm (0.2 in) long, and live on submerged wood; for example, piers, bridge piles, and ship hulls. Gribbles destroy the structures they infest by burrowing at close intervals into the members that make up the structure and consuming the wood from which they are made. Gribbles digest the wood with the help of an intestinal enzyme that breaks down cellulose, the chief constituent of the wood cell walls.
Shipworms, on the other hand, are of the Teredo family, and are marine, bivalve mollusks. However, like gribbles, shipworms, also have a reputation for causing substantial damage to wooden marine structures such as boat bottoms, piers and bridge piles. As their name implies, shipworms have wormlike bodies and feature disproportionately large siphons. While typically on the order of 10 inches in length or less, shipworm have been known to grow to as much as 2 feet or more in length and have diameters of half an inch. The shell valves of shipworms take the form of two small anterior members with file-like ribs, which are specialized for boring. By means of alternating contractions of the muscles that actuate the valves, the file-like ribs produce a cutting action that enable shipworms to bore into the wood they infest. Thereafter, they consume the structure by digesting the cellulose of the wooden members that make up the structure.
Over time, two principal approaches have emerged for dealing with marine borers. One has been to attempt to poison bores that seek to infest marine structures by impregnating the structure's wooden members prior to fabrication with pesticidally effective chemical agents. Chemical agents reported effective against gibbles and shipworms include: water-soluble alkali arsenates such as ammonia, sodium and potassium arsenite alone or as further compounded with copper or copper and zinc. Additionally, mixtures of copper naohthenate and Cellosolve together with crystal violate, malachite green oxalate or tributyltin oxide have been reported as effective. Still further, yet others have noted that such additives as dibutylbenzylphenol and chlorothalnil, in suitable amounts can be effective as well as the old standby creosote with coal tar.
The use of poisonous, chemical agents, however, is of limited effectiveness and has associated negative side effects. First, impregnating marine timbers and piles is a costly and cumbersome process. Because of the size of the timbers and piles, not only are there large volumes of wood to be treated which require large amounts of chemical agent be used, but additionally, because of their size, the timbers and piles are difficult and expensive to handle for purposes of impregnation. As a result, impregnation, typically, can not be economically carried out once a structures has been built and is in place. Additionally, if used, additive agents are susceptible to being leached from the wooden members by the washing action of the tidal zone. As a result, the agents tend to have a limited effective life. Accordingly, impregnation, typically, is not a viable approach for resolving borer infestation problems once they arise. Still further, the use of chemical agents has the very negative side effect of putting toxic materials into the Nations waterways--a result inconsistent with today's objectives for ecological conservation.
As a second approach to avoiding the effects of marine bore attack, workers seeking to control them have found they can be killed by suffocation. Specifically, biologists have noted that gribbles and shipworms rely on contact with sea water to get the oxygen they require for survival. Accordingly, marine engineers have proposed and devised a number of schemes of varying effectiveness for interrupting the supply of sea water to the structural members bores infest. And, where seal is effected the result is not only are borers suffocated and killed, but also, a barrier is established which prevents return of the creatures for as long as the seal can be maintained.
Regrettably, however, though a variety of schemes have been proposed for suffocating marine borers, still problems remain. For example, some engineers have proposed wrapping marine structural members with plastic sheeting, while others have suggested the application of split tubing, and still others, jacketing and subsequent filling with mud, cement or epoxy. However, each of these approaches, requires the marine member be "uninterrupted" along the length to be protected, so that the covering which is typically put on in overlapping fashion, can be applied and sealed. While these approaches can be effective when used on piles having continuous, water-exposed surfaces; that is, surfaces which are not interrupted by the other structural members such as planking or reinforcing elements, from the mud line to the high-water line, they do not work well where the surface is interrupted; as for example, on the timbers that form the pile caps of piers and docks, and interrupted piles, such as those positioned next to walls or other structures. In the case of pile-cap timbers, the timber surfaces are interrupted both at their lower faces by the piles upon which the cap timbers rest and at their upper faces by the decking or planking of the pier or dock they support. As a result it is not possible to effectively wrap them.
Still further the noted approaches have yet other drawbacks specific to the particular, respective scheme. With regard to pile wraps, a representative illustration is presented in U.S. Pat. No. 5,516,236 issued to Williams et al. As described in the Williams et al. patent, plastic sheeting such as polyethylene, is wrapped around the circumference of a pile in overlapping fashion, at least at the longitudinal end, and mechanically sealed to the pile with neoprene strips, nails and/or straps. Though the wrap can be effective in keeping water from the covered portion of the pile, in addition to requiring the surface wrapped be uninterrupted, the integrity of plastic sheeting and mechanical seals have been found susceptible to damage from objects in the water; for example, floating debris such as drift wood, bottles and the like which may be driven against the covered piles by wave action and winds. As well, because of their light weight, wraps are subject to damage from boats that may moor to the protected dock and pier piles--and also from plain vandalism. Additionally, because of nonuniform pile diameter over pile length arising from natural run out or erosion, folds and wrinkles, typically, arise in the wrap either when first applied or over time which are susceptible to cracking and rupture from continuous wave action. Yet further, pile wraps because of their light-weight character offer little in the way of reinforcement for pile strength that have been significantly eroded as a result of borer action.
As an alternative to plastic wraps and their light gauge, it has been proposed that higher-weight, split tubing be used. As described in U.S. Pat. No. 4,697,957 issued to E. D. Hellmers, to overcome some of the difficulties associated with light-gauge, plastic sheeting such as ease of damaging and wrinkling, it has been proposed that a longitudinally split length of heaver gauge, extruded hexene-ethylene tubing be applied to the pile. As described by Hellmers, the tubing is selected to have a diameter slightly larger than the pile, so that longitudinal split tubing can be overlapped at its split longitudinal ends and nailed in place. Additionally, Hellmers proposes that the split ends be pulled tightly; as for example with nylon webbing encircling the tube to effect seal. As noted, however, because of its cylindrical character tubing is not suitable for interrupted marine members such as pile caps. Additionally, because of the less resilient nature of the tubing material, creation of an effective seal can be difficult. And, the ability to get effective overlap and seal is rendered more problematic where the diameter of the pile varies over its length as a result of either natural run out or erosion. Still further, once again, though of heaver weight, split tubing also affords only a limited capacity to rehabilitate borer eroded piles.
Continuing, while the previously described designs require the marine member to be protected be unobstructed, an approach has been proposed that would be applicable to obstructed marine members having generally flat surfaces as might be found on pile caps and the like. However, because of its makeup, a number of the shortcomings noted in connection with the previously described approaches are again present. Particularly, U.S. Pat. No. 3,870,009 issued to Liddell, describes a protective covering recommended for use on submerged marine structures such as barges pontoons, piers, and bulkheads. As proposed by Liddell, the covering features waterproof flat sheeting of plastic, synthetic fabric or thin metal, and a network of battens that form a lattice of individually sealed modules for protecting the structure form borer attack. As described, in preferred form, synthetic material such as polyvinyl chloride, polyethylene or polyurethane is flatly extended in either single or multiple modular unit sheets over the surface to be protected, and fastened at unit boarders in sandwich fashion between an underlying sealing strip of neoprene, rubber of the like, and an overlying, lattice strip or batten of wood, metal or synthetic material with corrosive resistant nails.
Regrettably, however, as in the case of pile wraps, because of the thinness of the sheeting material, the structure is susceptible to damage from floating marine debris, wave and wind action, marine navigation and vandalism. Additionally, the seal for the sheeting is also vulnerable to damage. Because the seal structure requires use of an underlying strip, a waterproof sheet, and a batten seal sandwich, the seal regions of the assembly project substantially away form the surface it is mounted to, rendering it open to damage from floating marine debris, marine navigation and vandalism. Finally, and again as in the case of pile wraps, the structure offers little in the way of rehabilitation for borer deteriorated structures.
While the approaches of pile wraps, split tubing and plane sheeting are lacking in facility for rehabilitating eroded piles and capacity to withstand physical abuse, the noted approach of jacketing is substantially more effective in those areas. Regrettably, however, though jacketing provides improved durability and capacity for rehabilitation, it does so at a substantial increase in cost and complexity, and while still requiring the surface to be protected be uninterrupted. An example of pile jacketing is provided in U.S. Pat. No. 4,306,821 issued to Moore. In accordance with the Moor approach, a flexible, plastic or fiber glass rectangular sheet is positioned about and spaced from a pile by rubber or the like upper and lower seals, the sheet being nailed to the seals and underlying pile. A tongue-and-grove end coupling enables the longitudinal ends of the sheet to be joined, so as to close the cylinder. As proposed by Moore, the upper seal is circumferential discontinuous so that a heaver-than-water, liquid epoxy or other suitable filler can be poured into the cylindrical form to displace the water and fill the portions of the pile eaten away by borers. Following the setup of the filler the jacketing can be optionally removed. Also, in accord with the Moore teaching, prior to application of the jacket, the borer eroded pile must be properly prepared to assure the filler will adhere to the pile. For this purpose, Moore requires the eroded pile be sand blasted to clean off debris and foreign matter so that the heaver-than-water filer can adhere and remain in place once the filler hardens.
As noted, though jacketing provides for more effective rehabilitation of eroded piles, the required elaborate cleaning of the pile surface, the positioning of the form, and the specialty filler make for a more complex, time consuming and expensive process to perform and structure to build. Yet further, where adherence of the filler to the pile is either not effected, or subsequently disrupted, water communication and associated bore activity may continue. And, as pointed out, because of the need for unobstructed surface, jacketing is not convenient for use on pile cap timbers.